The invention relates to a method of identifying a protocol data unit in a network layer of an air interface in a cellular radio network, the network layer comprising a connection management sublayer and a mobility management sublayer, and the protocol data unit comprising a header which includes a protocol discriminator, some of the protocol discriminator values being allocated to the identification of protocol data units in the connection management sublayer and the mobility management sublayer.
The above described arrangement can be used in GSM systems. In new systems developed on the basis of the GSM system, such as the UMTS (Universal Mobile Telephone System), the introduction of new sublayers causes problems because new fields must then be added to the protocol data unit in order to allow the protocol data units of the new sublayers to be identified. This increases the size of the protocol data units.
An object of the invention is thus to provide a method and an equipment implementing the method which allow the above problems to be solved. This is achieved with a method described in the preamble, characterized in that at least one unreserved value of the protocol discriminator is used for identifying protocol data units in a radio network sublayer.
The invention also relates to a cellular radio network comprising a base station system, and a mobile station communicating with the base station system over an air interface, identifying means for identifying a protocol data unit in a network layer of an air interface by processing the protocol discriminator included in the header which the protocol data unit comprises, some of the protocol discriminator values of the identifying means being allocated to the identification of protocol data units in the connection management sublayer and the mobility management sublayer included in the network layer.
The cellular radio network of the invention is characterized in that the identifying means are arranged to use at least one unreserved value of the protocol discriminator for identifying protocol data units in a radio network sublayer.
The invention further relates to a protocol data unit in a network layer of an air interface in a cellular radio network, the network layer comprising a connection management sublayer and a mobility management sublayer, and the protocol data unit comprising a header which includes a protocol discriminator, some of the protocol discriminator values being allocated to the identification of protocol data units in the connection management sublayer and the mobility management sublayer.
The protocol data unit of the invention is characterized in that at least one unreserved protocol discriminator value is allocated to the identification of protocol data units in a radio network sublayer.
The preferred embodiments of the invention are disclosed in the dependent claims.
The invention is based on the fact that in the GSM system, some of the protocol discriminator values are not reserved for any purpose of use, so in further development work the values are available for the identification of new protocol data units.
The method and system of the invention provide various advantages. Since new fields need not be added into a protocol data unit for identification purposes, the protocol data unit does not grow bigger. This saves valuable radio capacity in the air interface. The changes involved also conform to GSM specifications.